Resistance Gene Profile and Serotype Distribution Mechanism of Erythromycin-Resistant Streptococcus Agalactiae Isolated from Infants and Young Children

Wei Ying; Guo Yan; Zhu Liqiang

doi:10.3969/j.issn.1004-5775.2025.24.002

Abstract：Objective:To investigate the mechanisms underlying the distribution of erythromycin resistance genes and serotypes in Group B Streptococcus(GBS)isolates from infants and young children.Methods:93 GBS-positive infants and pregnant women at 35～37 weeks gestation identified at Shenzhen Nanshan District People's Hospital from May 2022 to June 2023 were enrolled as study subjects.Samples encompassed multiple clinical specimen types including blood,cerebrospinal fluid,and respiratory secretions.The drug resistance gene spectrum and serotype distribution mechanisms of GBS were investigated in depth through specimen collection and processing,GBS isolation and identification,drug susceptibility testing,genotyping and drug resistance gene detection,and statistical analysis.Results:The resistance rates of GBS in infants and young children to erythromycin and clindamycin were 82.8%and 74.2%,respectively.Among pregnant women and mothers,GBS exhibited resistance rates of 91.1%to tetracycline and 58.9%to clindamycin.In resistance gene detection,78 strains were detected the erm(B)gene(83.9%detection rate),65 strains were detected the mef(A)gene(70.0%detection rate),and 60 strains simultaneously were detected both erm(B)and mef(A)genes(64.5%detection rate).There were significant differences in the carriage of antibiotic resistance genes among GBS serotypes,with serotypes Ⅲ and Ⅰa exhibiting higher rates of erythromycin resistance.Genotyping results revealed that ST-17 GBS demonstrated an erythromycin resistance rate as high as 92.3%,with all isolates carrying the erm(B)gene and 85.7%additionally harboring the mef(A)gene.Conclusion:The resistance gene spectrum of GBS in infants and young children is complex and diverse,with primary resistance mechanisms including target site modification and efflux pump-mediated efflux.Among these,the erm(B)gene and mef(A)gene are the predominant resistance genes.Different GBS serotypes exhibit distinct patterns of resistance gene carriage,and specific serotypes show a strong association with particular resistance genes.